#include <stdio.h>
#include <math.h>


double add (double a, double b) {
  return a + b;
}

double substract (double a, double b) {
  return a - b;
}

double multiply (double a, double b) {
  return a * b;
}

double divide (double a, double b) {
  return a / b;
}

double square (double x) {
  return x * x;
}

double circle_area (double radius) {
  return M_PI * square(radius);
}


int main () {
  double operand1;
  double operand2;
  // char

  printf("operand 1: ");
  scanf("%lf", &operand1);
  printf("operand 2: ");
  scanf("%lf", &operand2);

  printf("add: %lf\n", add(operand1, operand2));
  printf("substract: %lf\n", substract(operand1, operand2));
  printf("multiply: %lf\n", multiply(operand1, operand2));
  printf("divide: %lf\n", divide(operand1, operand2));

  printf("square: %lf\n", square(operand1));
  printf("circle area: %lf\n", circle_area(operand1));
  return 0;
}
